System and method for thermal processing casting material

ABSTRACT

A method for thermal processing rails including casting a rail from a metal, allowing the rail casting to cool to a temperature within a predetermined range, immediately placing the rail casting, when at the temperature, into a first chamber having gaseous nitrogen, cooling the rail casting to about −300 degrees using the gaseous nitrogen, allowing the rail casting to soak in a second chamber having liquid nitrogen and allowing the rail casting to reach room temperature.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present general inventive concept relates to a system and method for thermal processing of a metal casting work piece, and more particularly, to a system and method for thermal processing various types of metal casting work pieces, including iron and steel, using a continuous cooling process from a casting temperature to room temperature, without interruption and a high temperature heat treating step.

2. Background

Over the last several years, railway traffic has increased substantially. In addition, a rapid rise in weight and speed of trains has increased the wear rate of many rails, and therefore has led to an increasing demand for rails with improved material hardness, and abrasive wear resistance.

The utilization of thermal alteration of a material is well-known, a simple example comprising the tempering of ferrous alloys such as steel or cast iron wherein the hardness of the alloy is decreased, increasing ductility and toughness of the alloy. This is achieved, generally, by lowering the material below a critical lower transformation temperature altering the crystalline phases of the alloy.

Thermally tempering the material used to manufacture rails (steel) or altering the materials structure from an austenite structure into a microstructure that is stable at room temperature during a force-cooling process is known to harden the rail. Previously, these processes have been performed after the rail material has been allowed to cool to room temperature.

There are several conventional methods of force-cooling rail material including splash or spray cooling and submerging the rail into a coolant bath. However, using these methods may result in non-homogenous structural distribution over a cross-section as a function of rail length. Thereby The resulting lack of structural homogeneity throughout the rail material has a detrimental effect on the quality, wear rate, and hardness of the completed rail.

In addition, many of the devices used for these methods are not arranged in-line with rolling stands of a casting processes, which therefore necessitates an interruption and the need to stock rolled rails and a subsequent high temperature heat treatment process before proceeding to a thermal treatment. As such, these methods consume a considerable amount of energy, are inefficient, and produce a lower density rail.

Therefore, what is needed is a method and system for thermally processing cast metals, including iron and steel, immediately in-line with a casting process that continuously cools the cast metal, without interruption from the casting temperature, and that results in improved structural homogeneity, reduced wear rates, and increased hardness.

SUMMARY OF THE INVENTION

Certain of the foregoing and related aspects are readily attained according to the present general inventive concept by providing a method for thermal processing rails which includes casting a rail from a metal, allowing the rail casting to cool to a temperature within a predetermined range, immediately placing the rail casting, when at the temperature, into a first chamber having gaseous nitrogen, cooling the rail casting to about −300 degrees using the gaseous nitrogen, allowing the rail casting to soak in a second chamber having liquid nitrogen; and allowing the rail casting to reach room temperature.

Certain of the foregoing and related aspects are readily attained according to the present general inventive concept by also providing a system for thermally processing a metal casting which includes a transporting means configured to move a metal casting; and a plurality of chambers including a first chamber configured to store gaseous nitrogen and configured to receive the metal casting, a second chamber configured to store liquid nitrogen and configured to receive the metal casting, and a third chamber configured to bring the casting material to room temperature.

The transporting means may include a conveyor belt.

The transporting means continuously moves the metal casting through the first chamber, the second chamber, and the third chamber.

In contrast with conventional methods disclosed by the prior art, the present general inventive concept utilizes a thermal gradient using gaseous and liquid nitrogen to affect a desired temperature change, continuously and without interruption or requiring significant energy inputs as is conventionally performed, to the system immediately after a material, such as iron and steel is cast. This novel approach provides unexpected results in the physical characteristics of the casting, without the need for costly high temperature thermal processing as is conventionally used to such characteristics. In addition, the method according to the present inventive concept provides significantly improved wear resistance and increased hardness.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1A illustrates a front view of a conventional rail;

FIG. 1B illustrates a side view of the conventional rail illustrated in FIG. 1A;

FIG. 2 illustrates a flow chart of an exemplary method of thermal processing rail material using a thermal processing system according to present general inventive concept;

FIGS. 3A through 3H are schematic diagrams illustrating an operation of the method of thermal processing rail material within a thermal processing system according to an example embodiment of the present general inventive concept;

FIG. 4 illustrates a thermal processing system according to another example embodiment of the present general inventive concept; and

FIG. 5 illustrates a temperature vs. time chart illustrating the method of thermally processing rail castings illustrated in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventive concept will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the present general inventive concept are illustrated. The inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.

The present general inventive concept includes methods and systems for thermally processing rail castings that allows for the continuous cooling decent of rail castings from a casting temperature to about −300° F. and then to room temperature, without any interruption. In exemplary embodiments, the rail castings are allowed to cool to a temperature slightly below the casting temperature to about 32° F., prior to being placed in a first chamber containing gaseous nitrogen.

FIG. 1A illustrates a front view of a conventional rail and FIG. 1B illustrates a side view of the conventional rail illustrated in FIG. 1A.

Referring to FIGS. 1A and 1B, characteristics of conventional rails 10 with regards to geometrical profiles and mechanical properties are typically obtained by a sequence of thermo-mechanical processes including a hot rail rolling process followed by a thermal treatment and straightening step. The hot rolling process forms the geometrical profile of the rail and also provides the required metallurgical microstructure necessary for the following thermal treatment process. In particular, the hot rolling process allows the rail 10 to form fine microstructures which, in combination with the following thermal processing process, guarantees higher level of mechanical properties.

Conventionally, there are four different methods used to perform thermal treatment of rails including immersion of the rail 10 into a water tank, spraying the rail 10 with water, spraying the rail 10 with air, and spraying the rail 10 with an air/water mist.

In alternative embodiments, the present general inventive concept provides a method of thermally processing rails, without using a high-temperature thermal hardening process conventionally known and used.

FIG. 2 illustrates a flow chart of an exemplary method 100 of thermal processing rail material using a thermal processing system according to present general inventive concept.

In the present embodiment, the method 100 includes obtaining a castable metal which may include iron, steel, or various other castable metals, at step 102. In alternative exemplary embodiments, the castable metal may include conventionally known metals used to manufacture rails 10. However, the present general inventive concept is not limited thereto.

Next, at step 104, a rail casting 10 is then prepared from the obtained metal. The present general inventive concept may include any method conventionally known or used to cast rails, including castings from dies, sand, ceramic lost wax, and/or plaster based materials. However, the present general inventive concept is not limited thereto. The present general inventive concept will be described using the sand casting method for illustration purposes only. That is, the method according to the present general inventive concept may be performed using castings created from the various methods illustrated above.

Next, at step 106, once the rail 10 has been cast, the rail casting 10 is allowed to cool to a temperature between a predetermined range, while remaining within the sand or die. The predetermined range may be from slightly below the casting temperature of the obtained castable metal to about 32° F. In exemplary embodiments, the predetermined range may range between 600° F. to 100° F. In further exemplary embodiments, the predetermined range may range between 200° F. to 400° F. This process may take between 10 to 48 hours depending on a cross-sectional thickness of the rail casting 10. However, the present general inventive concept is not limited thereto.

Next, at step 108, the rail casting 10, at about 300° F. for example, is then placed within a first chamber containing gaseous nitrogen to continue the cooling decent of the rail casting to about −300° F. in a continuous, controlled, and uninterrupted manner. As such, the rail casting 10 is cooled continuously, without interruption, from an eutectoid temperature of about (2000° F. to 2750° F.) to about −300° F. That is, at step 108, the rail casting 10 is continuously cooled from about 300° F. to about −300° F. within the first chamber using gaseous nitrogen, without interruption.

Each castable metal has different eutectoid and/or casting temperatures. For illustration purposes, iron is described as having eutectoid or casting temperature of about 2750° F. and steel is described as having an eutectoid or casting temperature of about 2500° F. However, the present general inventive concept is not limited thereto.

Next, at step 110, the rail casting 10, is then moved into a second chamber containing liquid nitrogen and allowed to soak for a predetermined period of time. In the present embodiment, the metal casting 10 is allowed to soak for between 1 second to about 48 hours. However, the present general inventive concept is not limited thereto.

Next, at step 112, the rail casting 10 is then allowed to return to room temperature (i.e., about 72° F.). In the present embodiment, the rail casting 10 may be raised in an upward direction in order to help facilitate arriving at room temperature. However, the present general inventive concept is not limited thereto.

FIGS. 3A through 3H are schematic diagrams illustrating an operation of the method of thermal processing rail material 100 within a thermal processing system 200 according to an example embodiment of the present general inventive concept.

In the present embodiment, the thermal processing system 200 processes metal castings 10 directly from a casting temperature (e.g., about 2500 to 2750° F.) to about −300° F. and then to room temperature (e.g., about 72° F.), continuously without interruption. This new and novel method provides significant and unforeseen results in physical characteristics of the completed rail 10. For instance, rails 10 processed using the method 100 according to the present general inventive concept produced a 300% improvement when using an ASTM pin on disc test as compared to rails produced without the method 100. That is, the continuity of cooling decent of temperature of the rail casting 10 from eutectoid or casting temperature to −300° F., substantially increases the materials hardness, abrasive wear resistance, density, and wear life.

Referring to FIG. 3A, the thermal processing system 200 includes an insulated chamber 210 having an upper end 210 a and a lower end 210 b. The insulated chamber 210 includes a first chamber 212 (or temperature zone) containing gaseous nitrogen, a second chamber 214 (or temperature zone) containing liquid nitrogen, and a third chamber 216 (or temperature zone) at room temperature (i.e., about 72° F.).

The rail casting 10 is heated to a casting temperature of about (e.g., about 2500 to 2750° F.) and a cast is prepared. The rail casting 10 is then allowed to cool to a temperature T1 within a predetermined range as described above. The rail casting 10 is then moved to the first chamber 212 to continue cooling the rail casting 10 from the temperature T1 to temperature T2, wherein temperature T2 is about −300° F. The rail casting 10 is then soaked within the second chamber 214 having liquid nitrogen for about 1 second to about 48 hours. The rail casting 10 is then allowed to heat up to room temperature within the third chamber 216. In alternative embodiments, the third chamber 216 may be inclined with respect to the second chamber 214 and includes a means for transporting the rail casting 10 from the second chamber 214 to a higher elevation to arrive a room temperature.

For instance, in an example, referring to FIGS. 3A through 3G, once a rail casting 10 has been prepared and allowed to cool to about 300° F., the rail casting 10 is then placed into the first chamber 212 or otherwise exposed to gaseous nitrogen for about 24 hours until the rail casting 10 reaches about −300° F. (e.g., or −321° F.). The rail casting 10 is then placed into a second chamber 214 and is allowed to soak in liquid nitrogen for about 48 hours. Next, the rail casting 10 is brought back to room temperature by gradually raising or elevating the rail casting 10 along a y-direction or exposure to room temperature. However, the present general inventive concept is not limited thereto.

FIG. 4 illustrates a thermal processing system 300 according to another example embodiment of the present general inventive concept.

Referring to FIG. 4, the thermal processing system 300 includes an insulated chamber 310 having a first end 310 a and a second end 310 b. The insulated chamber 310 includes a first chamber 312 (or temperature zone T2) containing gaseous nitrogen, a second chamber 314 (or temperature zone T3) containing liquid nitrogen, and a third chamber 316 (or temperature zone T4) at room temperature (i.e., about 72° F.).

The rail castings 10 are moved within the insulated chamber 310 and exposed to gaseous nitrogen in a second temperature zone T2, liquid nitrogen in the third temperature zone T3, and room temperature in the fourth temperature zone T4. As illustrated, the rail casting 10 is raised in elevation to bring the rail casting 10 up to room temperature. However, the present general inventive concept is not limited thereto.

FIG. 5 illustrates a temperature vs. time chart illustrating the method of thermally processing rail material illustrated in FIG. 2.

In an exemplary embodiment, referring to FIG. 5, the obtained castable metal is heated to an eutectoid or casting temperature of about 2750° F. Immediately after the rail is cast, the rail casting 10 is allowed to cool to about 300° F. (step 106). Immediately after reaching about 300° F., the rail casting 10 is placed into a first chamber and cooled to about −300° F. using gaseous nitrogen. Immediately after reaching about −300° F., the rail casting 10 is then placed into a second chamber and soaked for about 40 hours in liquid nitrogen. Finally, the rail casting 10 is brought to room temperature within the third chamber, yielding a completely processed rail.

The methods and embodiments described above according to the present inventive concept removes the high temperature treating step required in conventional thermal processing methods, thereby significantly reducing manufacturing time and costs. The method according to the present inventive concept may be performed on Hadfield Steel as well as white cast iron thereby significantly improving the resistance to abrasion and Brinell hardness of all types of metals. The method according to the present inventive concept removes the high temperature treating step required in conventional thermal processing methods, thereby significantly reducing manufacturing time and costs.

While the present general inventive concept has been illustrated by description of several example embodiments, and while the illustrative embodiments have been described in detail, it is not the intention of the applicant to restrict or in any way limit the scope of the general inventive concept to such descriptions and illustrations. Instead, the descriptions, drawings, and claims herein are to be regarded as illustrative in nature, and not as restrictive, and additional embodiments will readily appear to those skilled in the art upon reading the above description and drawings. Additional modifications will readily appear to those skilled in the art. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept. 

What is claimed is:
 1. A method for thermal processing rails, comprising: casting a rail from a metal; allowing the rail casting to cool to a temperature within a predetermined range; immediately placing the rail casting, when at the temperature, into a first chamber having gaseous nitrogen; cooling the rail casting to about −300 degrees using the gaseous nitrogen; allowing the rail casting to soak in a second chamber having liquid nitrogen; and allowing the rail casting to reach room temperature.
 2. The method of claim 1, wherein the metal is iron.
 3. The method of claim 2, wherein the metal is steel.
 4. A system for thermally processing a metal casting, comprising: a transporting means configured to move a metal casting; and a plurality of chambers comprising: a first chamber configured to store gaseous nitrogen and configured to receive the metal casting; a second chamber configured to store liquid nitrogen and configured to receive the metal casting; and a third chamber configured to bring the casting material to room temperature.
 5. The system of claim 4, wherein the transporting means includes a conveyor belt.
 6. The system of claim 5, wherein the transporting means continuously moves the metal casting through the first chamber, the second chamber, and the third chamber. 